How Audio Compressors Work
A compressor is a very important item to have in your sound system arsenal, especially in a church or worship environment. A compressor is a device that controls the dynamic range of your input (guitar, vocals, piano, bass, etc…). When engineering sound for a church, you will note the dynamic differences that each song and song style may be. For this reasons, compressors come in handy big time. They can be used to add some extra punch to the instrument/mix; as well as some back bone to some looser sounding instruments, like the bass drum or piano. Also, a compressor can add sustain to instruments like guitar, or vocals. This can help enhance the realism of the signal. Setting up compressors can be a little confusing, but after you understand all of the required elements a little more you should have no problem.
How many Compressors should you have?
Ideally, you want to have as many compressors as you can get. Having each instrument and each vocalist compressed will even out your sound a lot. Being in control of every instrument is ultimately what every sound engineer is shooting for. However, if you do not have access to that many, you will want to compress your most important instruments first. If you only have two, a great start is by compressing your lead vocalist (worship leader). Regardless what you do after this, make sure he/she is compressed. This way you have control of the most important aspect of worship. Another instrument to start with is either the drums or the guitar. Both of these have a mixture of highs and lows that need to be controlled. If you have only one compressor, you can do one of two things. You can either compress the leader, or you can compress the whole mix.
A compressor has the same controls as gates do; the Threshold, Ratio, Attack, Release, and Output. Each control affects the next. The Threshold controls the point in which the compressor starts to reduce the audio level. You should always start at zero, and adjust from there. For example, if you set this to -10, the compressor activates sooner, which will compress sooner; giving you more control of your audio. Ratio is what adjusts how much compression takes place as the signal passes through the threshold. There would be no compression with a ratio of 1:1, because 1 DB of input would equal 1 BD of sound. So say we change this to 3:1, this would mean it now takes 3 DB of sound to equal 1 DB of output. A good starting point for your vocal input is 4:1. The more you adjust the ratio, the more the compressor becomes a limiter. Eventually you will turn the dial all the way to Infinity, a spot on the dial that limits all input volume to produce 1 DB of output.
The Attack dial on the compressor determines the speed the compressor compresses the signal as it passes through the Threshold. There will be LED lights that display this in an easy to read layout. The Release dial controls the speed the compressor returns the sound back to its original level. This is where you can add sustain to a vocalist or guitarist. Great for special equalizing! The last dial is Output. This measures the amount of output the compressor gives. With this, you can cover for the loss in volume you may have due to the compression.
This may seem like a lot of information to obtain, but it is all rather simple. There is no exact rule for setting up compressors, each church, auditorium, or sanctuary has different acoustics and instruments. Each sound tech must experiment with their own set up and find what works the best. Compressors are excellent for controlling dynamics of vocalists. They are also perfect for controlling the bottom end, (lower frequencies) of the bass drum, bass guitar, etc… If you can afford them, they are a great asset to have in your sound system! Experience and knowledge can be helpful by someone who can show you how its done.
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